Marshalling XML with Spring (How to handle referenced classes)

[Michael Bradshaw]

If I want to marshall a class to XML, and that class contains a reference to another class, how do I ONLY put the ID of that subclass in the XML. My simple example of this appears below. Say I have 2 classes, Employee & Department:

class Employee {
int id;
String lastName;
String firstName
String jobTitle;
Department department;
//getters and setters 
}

Class Department{
int id;
String name;
int departmentCode;
String departmentLocation;
//getters and setters 
}

Now suppose I’m building a RESTful interface and when I go to the URL http://www.mycompany.com/myApp/Employees/5
I want this to be displayed:

<Employee>
<ID> 5 </ID>
<LastName> Smith </LastName>
<FirstName> John </FirstName>
<JobTitle> Programmer </JobTitle>
<Department> 21 </Department>  <!—We just put the Department ID here, not the entire department object which includes department name, department code, etc-!!!->
</Employee> 

What is the best marshalling program in Spring to do this (JAXB, Castor, etc), and how do I do this? Does this have a name so that I can google for more information about it? Also, I would need to unmarshall the XML back to java, such that I get an employee with a reference to a department, but only the ID of the department would be filled.